The present invention relates to a dielectric ceramic composition to be used for dielectric layers of a multilayer ceramic capacitor having internal electrode layers composed of base metal such as nickel or the like, a capacitor using the same and a method of manufacturing the capacitor.
A conventional multilayer ceramic capacitor such as disclosed in Japanese Patent Laid-Open Publication No. 8-337471 (1996) is such that dielectric layers and internal electrode layers of nickel are alternately stacked, and sintered in an inert atmosphere or in a reducing atmosphere , and external electrodes are formed with silver or the like thereafter. The above-mentioned dielectric layers contain, as a main component, BaTiO3 in which rare earth oxide(s) such as Dy2O3 and the like and Co2O3 are contained, and contain BaO, MnO, MgO, Al2O3 and oxide glass mainly composed of Li2Oxe2x80x94(Si, Ti)xe2x80x94Al2O3 as sub components.
Generally, nickel and silver do not dissolve in each other. Accordingly, electrically connect the internal electrodes and the external electrodes without fail, it is preferable to form the external electrodes with, for example, copper or the like, a metal which dissolves completely in silver. However, to form with copper, the external electrodes should be formed in a non-oxidizing atmosphere. In the case of dielectric layers having the above-mentioned composition, the components of the dielectric layers are problematically reduced during formation of the external electrodes, and insulation resistance of the dielectric layers lowers accordingly.
Generally, in the case of manufacturing a multilayer capacitor using a dielectric ceramic composition mainly composed of barium titanate , when a molar ratio of Ba/Ti is less than 1, TiO2 is apt to be reduced during the sintering process in the reducing atmosphere, or while organic binders contained in the dielectric layers are burned. Although the reduced TiO2 is re-oxidized in some degree during a cooling process after sintering, the inside of each of the dielectric layers and the inside of each crystal grain resist being re-oxidized, and remain deficient in oxygen. As a result, the insulation resistance and dielectric breakdown voltage of the dielectric layers degrade.
An object of the present invention is to provide a dielectric ceramic composition enabling obtainment of a multilayer capacitor whose dielectric layers are not reduced , and have high insulation resistance even if external electrodes are formed of base metal such as copper or the like, a capacitor using this composition and a method of manufacturing the capacitor.
The dielectric ceramic composition of the present invention contains barium titanate as a main component, and contains at least 0.5 to 5.0 mol of Mg in the form of MgO, 0.1 to 3.0 mol of Dy in the form of Dy2O3, 0.01 to 0.4 mol of Mn in the form of MnO4/3, 0.01 to 0.26 mol of V in the form of V2O5, 0.3 to 3.5 mol of Si in the form of SiO2 and 0.01 to 3.0 mol of Al in the form of Al2O3 as sub components per 100 mol of the barium titanate, and is characterized in that a molar ratio of Ba/Ti ranges between 1.001 and 1.05.
The dielectric ceramic composition of the present invention compensates oxygen defect occurring during sintering with making the Ba/Ti molar ratio ranging between 1.001 and 1.05, the molar ratio which is made to be larger than 1, and with cation holes each being caused by substituting a part of Ti having a valence of four with V having a valence of five. As a result, reduction of TiO2 and decrease in insulation resistance of the dielectric ceramic composition can be prevented.